@@ -2729,6 +2729,37 @@ void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans)
btrfs_dec_delayed_refs_rsv_bg_inserts(fs_info);
list_del_init(&block_group->bg_list);
clear_bit(BLOCK_GROUP_FLAG_NEW, &block_group->runtime_flags);
+
+ /*
+ * If the block group is still unused, add it to the list of
+ * unused block groups. The block group may have been created in
+ * order to satisfy a space reservation, in which case the
+ * extent allocation only happens later. But often we don't
+ * actually need to allocate space that we previously reserved,
+ * so the block group may become unused for a long time. For
+ * example for metadata we generally reserve space for a worst
+ * possible scenario, but then don't end up allocating all that
+ * space or none at all (due to no need to COW, extent buffers
+ * were already COWed in the current transaction and still
+ * unwritten, tree heights lower than the maximum possible
+ * height, etc). For data we generally reserve the axact amount
+ * of space we are going to allocate later, the exception is
+ * when using compression, as we must reserve space based on the
+ * uncompressed data size, because the compression is only done
+ * when writeback triggered and we don't know how much space we
+ * are actually going to need, so we reserve the uncompressed
+ * size because the data may be uncompressible in the worst case.
+ */
+ if (ret == 0) {
+ bool used;
+
+ spin_lock(&block_group->lock);
+ used = btrfs_is_block_group_used(block_group);
+ spin_unlock(&block_group->lock);
+
+ if (!used)
+ btrfs_mark_bg_unused(block_group);
+ }
}
btrfs_trans_release_chunk_metadata(trans);
}